The accelerated corrosion tests of six squat shear walls with span ratio of 1.0 were conducted by artificial climate laboratory to understand the seismic performance of squat RC shear walls under offshore atmospheric environment. Their quasi-static experiments were implemented. The hysteresis loops regarding the relation between horizontal load and displacement of specimens with different axial compression ratio and various degrees of corrosion crack width were obtained. The skeleton curves of specimens were further achieved. Based on the test results, some performance aspects, such as the ultimate capacity, rigidity, ductility and energy dissipation capacity, were analyzed. The result shows that with the increase of axial compression ratio the bearing capacity and stiffness of corrosion specimens continued to improve, while their ductility and the deformation recovery capability are reduced. These manifest that the axial compression ratio must be strictly controlled during seismic design under offshore atmospheric environment. In addition, the crack load and the ultimate load, rigidity, ductility, energy dissipation capacity decrease with the increase of corrosion crack width of specimens. Moreover, when the specimen subjected to serious corrosion, the brittle failure is more obvious without any warning. Above findings demonstrate that with concrete ages growing over time, the internal rebar under this condition suffers increasingly severe corrosion and behaves worse in seismic performance.